In context of many downhole operations in a well, it is necessary to form holes through a pipe wall of one or more pipe bodies (or pipe strings) being more or less concentrically disposed in the well. As such, it may involve making holes through the pipe wall of casings, liners, production tubings or similar pipe bodies. This is oftentimes referred to as perforation of the pipe body.
For such perforation purposes, it is customary to use a perforation tool provided with explosive charges and being lowered into the particular pipe body from the surface of the well. Upon lowering such a perforation tool into the pipe body, the tool is typically mounted on a lower end of a connection line, which may be comprised of an electric cable, a coiled tubing string or a drill pipe string. Normally, such a perforation tool does not have to be anchored and centralized in the pipe string prior to activating detonation of the charges.
Further, such a perforation tool will normally be provided with so-called shaped charges, which typically are assembled and distributed according to a specific pattern on the perforation tool, the charges of which form, upon detonation, substantially circular holes through the pipe wall of the surrounding pipe body. Yet further, the explosive charges of the perforation tool may be activated and detonated via an electric signal or a pressure increase communicated to the tool from the surface of the well. Such perforation equipment constitutes prior art per se, hence is not discussed in further detail herein.
When using such explosive charges for perforation purposes in a well, it may prove difficult to control, with relatively good accuracy, the radial perforation depth outwards from the perforation tool. However, for some downhole operations, such as perforation of one or more pipe bodies for production or injection purposes, such a control of the perforation depth is of relatively little importance given that a greatest possible perforation depth oftentimes is desirable in such situations in order to achieve good fluid communication with the rocks surrounding the well.
On the other hand, a relatively accurate control of the perforation depth may be of great importance in a well where two or more pipe bodies (or pipe strings) are disposed more or less concentrically relative to each other, and where it is desirable only to form perforations (holes) through the pipe wall of the innermost pipe body in such a tubular constellation. Such a need may exist if desirable to clean and/or introduce, via such perforations, a treatment fluid, for example a fluidized plugging material, into an annulus located immediately outside the innermost pipe body, i.e. between the innermost pipe body and a next pipe body disposed more or less concentrically around the innermost pipe body. Methods for such perforation, cleaning as and plugging are described in WO 2012/096580 A1 and in WO 2013/133719 A1.
Given that perforation by means of explosive charges provides relatively poor control of said radial perforation depth, a need therefore exists in the industry for an alternative technical solution that is simple, operationally reliable and cost effective, and which renders possible to control said perforation depth in the radial direction outwards from an associated cutting tool when disposed in a pipe body in a well.
More specifically, a need exists for such an alternative technical solution rendering possible to make holes (perforations) only through the pipe wall of the innermost pipe body, and without perforating or significantly damaging the pipe wall of a surrounding, second pipe body in the well.